1. Field of the Invention
This invention relates to a method and apparatus for decoding an encoded signal obtained by orthogonal-transforming an input signal.
2. Description of the Related Art
There are a known variety of encoding methods in which audio signals inclusive of speech signals and acoustic signals are compressed by exploiting statistical properties of the audio signals in the time domain and in the frequency domain, as well as psychoacoustic characteristics of human beings. These encoding methods are roughly classified into encoding in the time domain, encoding in the frequency domain, and analysis synthesis encoding.
Video signals are often reproduced at speeds faster or slower than their recorded speed. It has been thought desirable that the speech signals associated with video signals be reproduced at a constant speed irrespective of the reproducing speed of the video signals. Ordinarily, if the speech signals are recorded synchronously with the video signals, and if the video signals are reproduced at one-half speed, the speech signals are also reproduced at one-half speed and, hence, are changed in pitch. Thus, it becomes necessary to perform signal compression along the time axis taking into account the zero-crossing point to restore the pitch of the speech signal to the pitch of the original signal at the standard reproducing speed.
High-efficiency speech encoding methods that perform time-axis processing as described above, for example, code excited linear prediction (CELP) encoding, allow fast modification along the time axis. Nevertheless, implementation of these methods has been difficult because of the large volume of processing operations required during decoding.